description = [[
Performs brute force password auditing against the BackOrifice service. The
<code>backorifice-brute.ports</code> script argument is mandatory (it specifies ports to run
the script against).
]]

---
-- @usage
-- nmap -sU --script backorifice-brute <host> --script-args backorifice-brute.ports=<ports>
--
-- @arg backorifice-brute.ports (mandatory) List of UDP ports to run the script against separated with "," ex. "U:31337,25252,151-222", "U:1024-1512"
--
-- This script uses the brute library to perform password guessing. A 
-- successful password guess is stored in the nmap registry, under the 
-- <code>nmap.registry.credentials.backorifice</code> table for other BackOrifice 
-- scripts to use.
--
-- @output
-- PORT       STATE  SERVICE
-- 31337/udp  open   BackOrifice
-- | backorifice-brute:  
-- |   Accounts:
-- |     michael => Valid credentials
-- |   Statistics
-- |_    Perfomed 60023 guesses in 467 seconds, average tps: 138
--

-- Summary
-- -------
--   x The Driver class contains the driver implementation used by the brute
--     library
--   x The backorifice class contains the backorifice client implementation
--

author = "Gorjan Petrovski"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = {"intrusive", "brute"}

require("nmap")
require("bin")
require("bit")
require("shortport")
require("brute")
require("stdnse")
require("creds")

-- This portrule succeeds only when the open|filtered port is in the port range
-- which is specified by the ports script argument
portrule = function(host, port)
	if not stdnse.get_script_args(SCRIPT_NAME .. ".ports") then
		stdnse.print_debug(3,"Skipping '%s' %s, 'ports' argument is missing.",SCRIPT_NAME, SCRIPT_TYPE)
		return false
	end

	local ports = stdnse.get_script_args(SCRIPT_NAME .. ".ports")

	--print out a debug message if port 31337/udp is open
	if port.number==31337 and port.protocol == "udp" and not(ports) then
		stdnse.print_debug("Port 31337/udp is open. Possibility of version detection and password bruteforcing using the backorifice-brute script")
		return false
	end
	
	return port.protocol == "udp" and stdnse.in_port_range(port, ports:gsub(",",",") ) and
		not(shortport.port_is_excluded(port.number,port.protocol))
end

local backorifice = 
{
	new = function(self, host, port)
		local o = {}
		setmetatable(o, self)
		self.__index = self
		o.host = host
		o.port = port
		return o
	end,
	
	--- Initializes the backorifice object
	--
	initialize = function(self)
		--create socket
		self.socket = nmap.new_socket("udp")
		self.socket:set_timeout(self.host.times.timeout * 1000)
		return true
	end,
	
	--- Attempts to send an encrypted PING packet to BackOrifice service 
	--
	-- @param password string containing password for encryption
	-- @param initial_seed number containing initial encryption seed
	-- @return status, true on success, false on failure
	-- @return err string containing error message on failure
	try_password = function(self, password, initial_seed)
		--initialize BackOrifice PING packet:   |MAGICSTRING|size|packetID|TYPE_PING|arg1|arg_separat|arg2|CRC/disregarded|
		local PING_PACKET = bin.pack("A<IICACAC", "*!*QWTY?",  19,       0,     0x01,  "",       0x00,  "",           0x00)
		local seed, status, response, encrypted_ping
		
		if not(initial_seed) then 
			seed = self:gen_initial_seed(password)
		else
			seed = initial_seed
		end
		
		encrypted_ping = self:BOcrypt(PING_PACKET,seed)
		
		status, response = self.socket:sendto(self.host.ip, self.port.number, encrypted_ping)
		if not(status) then
			return false, response
		end
		status, response = self.socket:receive()
		
		-- The first 8 bytes of both response and sent data are 
		-- magicstring = "*!*QWTY?", without the quotes, and since
		-- both are encrypted with the same initial seed, this is 
		-- how we verify we are talking to a BackOrifice service.
		-- The statement is optimized so as not to decrypt unless 
		-- comparison of encrypted magicstrings succeds
		if status and response:sub(1,8) == encrypted_ping:sub(1,8)
				and self:BOcrypt(response,seed):match("!PONG!(1%.20)!.*!") then
			local BOversion, BOhostname = self:BOcrypt(response,seed):match("!PONG!(1%.20)!(.*)!")
			self:insert_version_info(BOversion,BOhostname,nil,password)
			return true
		else
			if not(status) then
				return false, response
			else
				return false,"Response not recognized."
			end
		end
	end,
	
	--- Close the socket
	--
	-- @return status true on success, false on failure
	close = function(self)
		return self.socket:close()
	end,
	
	--- Generates the initial encryption seed from a password
	--
	-- @param password string containing password
	-- @return seed number containing initial seed
	gen_initial_seed = function(self, password)
		if password == nil then
			return 31337
		else
			local y = #password
			local z = 0

			for x = 1,y do
				local pchar = string.byte(password,x)
				z = z + pchar
			end

			for x=1,y do
				local pchar = string.byte(password,x)
				if (x-1)%2 == 1 then
					z = z - (pchar * (y-(x-1)+1))
				else
					z = z + (pchar * (y-(x-1)+1))
				end
				z = z % 0x7fffffff
			end
			z = (z*y) % 0x7fffffff
			return z
		end
	end,
	
	--- Generates next encryption seed from given seed
	--
	-- @param seed number containing current seed
	-- @return seed number containing next seed
	gen_next_seed = function(self, seed)
		seed = seed*214013 + 2531011
		seed = bit.band(seed,0xffffff)
		return seed
	end,
	
	--- Encrypts/decrypts data using BackOrifice algorithm
	--
	-- @param data binary string containing data to be encrypted/decrypted
	-- @param initial_seed number containing initial encryption seed
	-- @return data binary string containing encrypted/decrypted data
	BOcrypt = function(self, data, initial_seed )
		if data==nil then return end

		local output =""		
		local seed = initial_seed
		local data_byte
		local crypto_byte

		for i = 1, #data  do
			data_byte = string.byte(data,i)

			--calculate next seed
			seed = self:gen_next_seed(seed)
			--calculate encryption key based on seed
			local key = bit.band(bit.arshift(seed,16), 0xff)

			crypto_byte = bit.bxor(data_byte,key)
			output = bin.pack("AC",output,crypto_byte)
			--ARGSIZE limitation from BackOrifice server
			if i == 256 then break end 
		end
		return output
	end,
	
	insert_version_info = function(self,BOversion,BOhostname,initial_seed,password)
		if not self.port.version then self.port.version={} end
		if not self.port.version.name then 
			self.port.version.name ="BackOrifice"
			self.port.version.name_confidence = 10
		end
		if not self.port.version.product then self.port.version.product ="BackOrifice trojan" end
		if not self.port.version.version then self.port.version.version = BOversion end
		if not self.port.version.extrainfo then 
			if not password then
				if not initial_seed then
					self.port.version.extrainfo = "no password"
				else
					self.port.version.extrainfo = "initial encryption seed="..initial_seed
				end
			else
				self.port.version.extrainfo = "password="..password
			end
		end
		self.port.version.hostname = BOhostname
		if not self.port.version.ostype then self.port.version.ostype = "Windows" end
		nmap.set_port_version(self.host, self.port, "hardmatched")
		nmap.set_port_state(self.host,self.port,"open")
	end
}

local Driver =
{		
	new = function(self, host, port)
		local o = {}
       	setmetatable(o, self)
        self.__index = self
		o.host = host
		o.port = port
		return o
	end,
	
	connect=function(self)
		--only initialize since BackOrifice service knows no connect()
		self.bo = backorifice:new(self.host,self.port)
		self.bo:initialize()
		return true
	end,
	
	disconnect = function( self )
		self.bo:close()
	end,
	
	--- Attempts to send encrypted PING packet to BackOrifice service
	--
	-- @param username string containing username which is disregarded
	-- @param password string containing login password
	-- @return brute.Error object on failure
	--         brute.Account object on success
	login = function( self, username, password )
		local status, msg = self.bo:try_password(password,nil)
		if status then
			if not(nmap.registry['credentials']) then
				nmap.registry['credentials']={}
			end
			if ( not( nmap.registry.credentials['backorifice'] ) ) then
				nmap.registry.credentials['backorifice'] = {}
			end
			table.insert( nmap.registry.credentials.backorifice, { password = password } )
			return true, brute.Account:new("", password, creds.State.VALID)
		else  
			-- The only indication that the password is incorrect is a timeout
			local err = brute.Error:new( "Incorrect password" )
			err:setRetry(false)
			return false, err
		end
	end,
	
}

action = function( host, port )
	
	local status, result
	local engine = brute.Engine:new(Driver,host,port)
	
	engine.options.firstonly = true
	engine.options.passonly = true
	engine.options.script_name = SCRIPT_NAME
	
	status, result = engine:start()
	
	return result
end
